The present invention relates to pilot valves for hydraulic systems and, more particularly, to a pilot valve employing a thin metal strip which is rolled onto and off of the openings of a pair of restrictor paths to replace conventional nozzle openings.
An actuator valve system as used in a submarine for such uses as moving the diving planes is shown in simplified form in FIG. 1 and generally indicated as 10. A large, heavy duty actuator 11 having a piston ram 12 is connected by actuator rod 13 to the diving plane 14. As the actuator rod 13 is moved in the direction of the arrow 15, the diving plane 14 is rotated as indicated by the arrows 16. When the ram 12 and actuator rod 13 are held in a fixed position, the plane 14 is also held in its then attained position and resists movement therefrom. The motive and holding power for the ram 12 is provided by a hydraulic source 17. Because of the sizes, volumes, and pressures involved, the flow of hydraulic fluid between the source 17 and the actuator 11 through lines 18 (in the directions indicated by the arrows for "supply" and "return") is controlled by the high flow, four-way actuator valve 19 containing spool piston 20 sealably and longitudinally slideably disposed therein. As the spool piston 20 is moved in either direction, there is a corresponding change in the flow of hydraulic fluid to the actuator 11. Hydraulic lines 18 are connected at opposite ends of the cylindrical housing of actuator 11 and hydraulic fluid at changeable pressures P.sub.L and P.sub.R is introduced into the cylindrical housing to move the piston ram 12. When the pressures P.sub.L and P.sub.R are equal, the ram 12 remains in a static position. If pressure P.sub.L exceeds pressure P.sub.R, the ram 12 is moved to the right as FIG. 1 is viewed. Pressure P.sub.R exceeding pressure P.sub.L, of course, causes the ram 12 to move to the left as the picture is viewed.
In a system such as 10 used on submarines for moving diving planes and the like, it is quite typical to further interpose a pilot valve such as that indicated as 24 to control the input of hydraulic fluid to the actuator valve 19 so as to move the spool piston 20 in response to an electrical control signal. Such a prior arrangement is shown in FIG. 2. The working portions of a pilot valve according to the prior art are generally indicated as 24. Pilot valve 24 comprises a pair of opposed control nozzles 26 having a moveable flapper 28 therebetween. Each control nozzle 26 comprises an inlet pipe 30 through which the hydraulic fluid 22 (supplied by source 17 on line 18) enters. The fluid 22 passes through an orifice plate 32 which causes a fluid pressure drop depending on the velocity of the fluid passing therethrough. Past the orifice plate 32, the control nozzle 26 has an orifice outlet opening 34 disposed adjacent the moveable flapper 28 and an outlet pipe 36 which is adapted to connect to a respective one of the hydraulic input lines of the actuator valve 19.
As can be seen, the orifice outlet openings 34 are disposed in facing relationship on opposite sides of the moveable flapper 28. Flapper 28 is pivoted at 38 and can be moved in either direction, as indicated by the arrows 40, by the in and out movement of electrically driven motor armature 42 in response to an electrical control signal input on lines 44. As depicted in the enlarged drawing of FIG. 3, as fluid 22 under pressure P.sub.in attempts to exit through the orifice outlet opening 34, the positioning of the flapper 28 tends to impede the flow of fluid 22 through opening 34, depending upon the positioning of the flapper 28. The closer the flapper 28 is to the outlet opening 34, the greater the back pressure created upon hydraulic fluid 22. This, in turn, causes the flow rate through the orifice plate 32 to decrease and the pressure within the outlet pipe 36 to increase. As the moveable flapper 28 is moved by the electrical actuator 42 away from an outlet opening 34, the hydraulic fluid 22 can move more easily therethrough, the flow rate through the orifice plate 32 increases, and the pressure within the outlet pipe 36 decreases. The symmetrical and opposing arrangement of the nozzles 26 with the flapper 28 results in an output differential pressure (the absolute value of P1-P2) which is a function of the motion of flapper 28. The differences (or identity) in pressures P1 and P2 which are applied on opposite ends of the spool piston 20 cause piston 20 to be moved or held stationary just as ram 15 was controlled by pressures P.sub.L and P.sub.R.
Within a modern nuclear submarine, the foregoing operation of the prior art pilot valves causes two problems. First, there is a constant flow of hydraulic fluid 22 through the orifice outlet openings 34 of the control nozzles 26. Thus, there is always an amount of leakage hydraulic fluid 22 passing into a sump region which must be recycled. Additionally, the flow of the hydraulic fluid 22 through the control nozzles 26 is noisy. Noise, of course, is undesirable since it allows enemy vessels to locate and track the submarine.
Wherefore, it is the object of the present invention to provide a pilot valve for use in hydraulic systems, primarily for use aboard submarines, in which the steady state leakage problem is virtually eliminated and in which the noise attendant to the operation thereof is reduced to a minimum.